Earlier quoted context omitted.
You’re burying the lede here, which is that the Delaware Chancery Court rules that Tesla had paid a fair price for Solar City: https://www.businessinsider.com/elon-musk-wins-solarcity-tes...
Arguably we'll never know. A court ruling that it's a fair price isn't the same as letting the market decide
That is, the standard the defendants have to meet (not the plaintiffs, the burden is actually on tesla here despite having been sued) is that the transaction was entirely fair to the corporation and shareholders- the process was a fair one, the price was a fair one, etc.
I have trouble thinking of a case where you can prove all this[1] but the market would have come up with something different. Almost by definition, if the market would have decided to pay a lower price, either the price or the process was probably not fair.
[1] Which again, you have to do affirmatively. You aren't just rebutting plaintiff evidence, the burden is on you to show the fairness